The present application is a request for renewal of our current chemo- prevention trial CA 31711, "Chemoprevention in Polyposis". The original objectives were to establish a randomized, double-blind controlled clinical trial in a defined population at risk for large bowel cancer (e.g. patients with familial polyposis), and to determine whether supplementation of the diet with ascorbic acid and alpha tocopherol or fiber might favorably affect the number and size rectal polyps in these patients. The original goals with respect to patient accrual, completed in November 1983, have been met. Patients are examined every 3 months. At each visit we (1) assess polyp number, area, and location (2) evaluate compliance by interview and laboratory tests (3) collect information about dietary intake and (4) evaluate by hematologic tests the safety or toxicity of treatment. Initial data have also been gathered in the areas of (1) psychosocial aspects and (2) genetic analysis. The goals, then, of the proposed study are to continue the current trial, designed as a phase II/III cancer control study, according to the original format with an additional six months for patient followup and data analysis. We plan to: (1) continue the clinical assessment of polyposis patients until all patients have been on treatment for a minimum of 48 months; (2) develop an extended polyposis registry and pedigree analysis of patients and their families; (3) assess the psychosocial and emotional status of patients and their families. These findings will guide our team in improving participation and compliance and providing genetic and psychological counseling; (4) evaluate biochemical determinants as predictive indices of precancer. We will continue to use the 3H-thymidine labelling index and will also develop ornithine decarboxyhlase enzyme activity profiles in biopsies of the patients' rectal mucosa. (5) Establish the reliability of video-endoscopic techniques as a means of objectivley assessing rectal polyps. Using these results, we will evaluate the feasibility and design of an expanded chemoprevention trial for patients with this inherited precanceous condition.